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This document relates to an organic light emitting diode device, and more particularly, to an organic light emitting diode device which can achieve high emission efficiency and low driving voltage.
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Image display devices used for displaying a variety of information on a screen are one of the core technologies of the information and communication era. Such image display devices have been being developed to be thinner, lighter, and more portable, and furthermore to have high performance. With the development of the information society, various demands for display devices have been increasing. To meet these demands, research on flat panel displays such as liquid crystal displays (LCD), plasma display panels (PDP), electroluminescent displays (ELD), field emission displays (FED), organic light emitting diodes (OLED), etc has been actively conducted.
Among the flat panel displays, the OLED devices are a type of devices that emit light as electrons and holes are paired and extinguished, when a charge is injected into an organic light emitting layer formed between an anode and a cathode. The OLED devices are advantageous in that they may be formed on a flexible transparent substrate such as plastic, and are operable at relatively low voltage as compared to plasma display panels or inorganic EL displays, consume less power, and give good color balance. Especially, white OLED devices are used for various purposes in lighting, thin light sources, backlights for liquid crystal displays, or full-color displays using color filters.
In the development of white OLED devices, high efficiency, long lifetime, color purity, color stability against current and voltage variations, ease of manufacturing, etc. are important, so research and development are being done depending on which of these factors should be taken into account. White OLED device structures may be roughly classified into a single-layer emitting structure and a multilayer emitting structure. Of these structures, a multilayer emitting structure having a blue fluorescent emitting layer and a yellow phosphorescent emitting layer stacked in tandem is mainly employed to realize white OLED devices with long lifetime.
Specifically, a phosphorescent emitting structure is used, which is a lamination of a first light emitting part using a blue fluorescent diode as a light emitting layer and a second light emitting part using a yellow phosphorescent diode as a light emitting layer. Such a white OLED device produces white light by mixing blue light emitted from the blue fluorescent diode and yellow light emitted from the yellow phosphorescent diode. In this case, a charge generation layer is formed between the first light emitting part and the second light emitting part to double the efficiency of current generated in the light emitting layers and facilitate charge distribution. The charge generation layer is a layer that generates a charge, i.e., electrons and holes, in it, which can prevent a rise in driving voltage because it doubles the efficiency of current generated in the light emitting layers and facilitates charge distribution.
However, the currently used charge generation layer focuses on maximizing the injection of holes and electrons into each emitting layer, but with the limitation that the transfer of electrons from the charge generation layer to an electron transport layer is not smooth. Poor electron injection may result in poor balance between electrons and holes, causing a reduction in the efficiency of the light emitting layers and therefore a degradation of the device characteristics.